Manufacture of waterlaid felts and impregnated products prepared therefrom



Patented June 5, 1934 l,96l,945 v PA-TENT OFFICE I MANUFACTURE OF WATERLAID FELTS AND v IMPREGNATED PRODUCTS PREPARED THEREFROM Milton 0. Schur and Walter L. Hearn, Berlin, N. H., assignors to Brown Company, Berlin N. IL, a corporation of Maine No Drawing.

23 Claims.

This invention relates to the'manufacture of waterlaid felts more especially of a character "designed for] impregnation purposes, and to the impregnated'products prepared from such felts. In making waterlai'd' felts for impregnation purposes, it has been estab'ished that refined wood pulps constitutean advantageousraw .material, particularly when such pulps are used in a substantially unhvdrated'state. Indeed, it has been established that through the use of refined, substantially unhydrated wood pulpsas raw material, it is possible to arrive at impregnated sheets having a surprisingly valuable combination of characteristics, even though the raw or unlmpregnated felts made from such fibers may be tender and lacking in much strength or tear resistance. For instance, bituminized sheets containing such felt bases possess unusually high resistance to tear, and pliancy or flexibility.

We have found that in making feltscontaining refinedwood pulp or the like as the princ'palraw material, it is decidedly advantageous to incorporate pulverulent binders into the felt--' making furnish. While, various pulverulent casein, or the like may be employed in accordance with our invention, we have found that a starchy material, such as raw potato starch, constitutes a binder which is preferable from both a technical and economic standpoint. Thus, raw potato starch is not only a comparatively inexpensive binder, but is made up of grains sufilcientlyicoarse to be retained by the bulk feltmaking stock with but little loss in the white water drained from the felt-making machine. .During the drying of thefelt at elevated tomperature on the drying end of the felt-making machine, the starch granules are gelatinized to afford the desired bonding action on the fibers of the felt.

The foregoing principle of introducing a pulverulentbinder into the felt-making furnish may bepractised to advantage when the furnish is made up entirely of substantially unhydrated, refined wood pulp, but it is especially valuable ,when the furnish contains, in addition to a preponderant proportion of such wood pulp, a subordinate proportion of beaten rags or rag halfstufi, as disclosed in our application Serial No.

' 643,544, filed November19, 1932. The presence of rag pulp greatly improves the characteristics of the felt, as pointed out in that application.

' The presence of binder in the felt is of value, in that it inhibits cracking,or breaking tend- .encies in the felt, and more especially cracking binders of the nature of powdered dry glue,

7 Application November 19, 1932, Serial No. 643,545

or breaking resulting from the parting or separation of'the surface fibers'from oneariother when the felt is flexed. Such cracking or breaking tendencies are especially prevalent in felts wh'ch are made entirely of substantially unhydrated wood pulp and which are of comparatively low compactness, as in such case'the fibers are not tied or bonded together to'any pronounced degree, and are hence free to separate under fiexure which places them under substantial tension. In accordance'wlth the present invention, on the other hand, the fibers of the felt are bonded together through the use of binder in such amount: as will permit the felt to be flexed withoutcracking about a mandrel of a diameter as low as 2 ",inches.' The attainment of this result means that the binder should be used in restricted amount, .for if too much binder is employed, the felt may become so stiif and brittle as to acquire cracking or breaking. tendencies on this account. The fact is, that we prefer to use a starchy binder of the nature of raw potato starch, tapioca, flour, dextrin, or the like, in amount not. exceeding about 10% by weight of the,dry fibrous material entering into the feltmaking furnish.

The felts of the present invention may be impregnated with various secondary binders to pro- 'duce'finished products possessing an advantageous combination of characteristics. Thus, the may be impregnated quickly and'uniformly with various binders, such as latex, natural and synthetic resins, cellulose i ester solutions, waxes, bitumen, or other binders of a thermoplastic, water-dispersed, or dissolved variety. While not limited thereto, we shall hereinafter deal with our invention as applied to the manufacture of bituminized sheets of a character highly prized in the roofing and flooring industries. In both these industries, waste rags have heretofore been employed as the raw material in making the felt base, which is bituminized and put through the finishing operations. In the roofing industry, the bituminized sheet is surfaced with talc, sand, mica, or the like, when roll roofing is in view, or is coated with blown asphalt and then surfaced with crushed slate or similar granular material when roofing shingles'are in view. In the flooring industry, the bituminized sheet is put through a printing or painting machine, which applies an ornamental coating to the sheet. In both these industries, the finished article has heretofore been easy-tearing and of poor pliancy or flexibility. V

A specific example of procedure falling within the purview of our invention and applicable in the manufacture of roofing and flooring materials, may be practised substantially as follows. The usual rags currently employed in making roofing and flooring felts may be used in amount up to about 50% by weight of the fibrous furnish prepared in the beater engine. The rags may contain some wool fiber in addition to the cotton. The usual hollander may be charged with the rags and sufficient water to ensure circulation,'whereupon beating of the rags may be carried on until the fibers have been reduced to the desired extent and an aqueous pulp suspension fit for felt-making has been produced. The beater roll may then be raised from the bed-plate and the refined wood pulp may then be added to the rag halfstuff and the engine kept running until a physically homogeneous mixture of the two kinds of fiber has been effected. While the engine is thus running, raw potato starch may be added in amount up to about 10% by weight of the mixed fibers. The starch thus becomes uniformly disseminated throughout the mixture. The refined wood pulp is thus kept in a substantially unhydrated state by reason of the fact that the beater roll is operated merely to effect-a mixing of such pulp with the previously beaten rags,'an d further by reason of the fact that refined wood pulp is comparatively difiicultly hydratable. The mixed fiber furnish containing the binder is delivered from the beater engine into the stock chest, wherein it is diluted to the appropriate consistency for delivery to the felt-making machine. The diluted pulp is further thinned with large volumes of water, most of which is white water recirculated from the forming or wet end of the felt machine. It is highly desirable that pulp be fed onto the felt-forming screen and/or wire cloth in a highly diluted state, in order that good formation shall be obtained. In the case of a cylinder mould, for example, it is preferred to operate at consistencies below, say, about 0.35%, in order to avoid lumpy felt formation. The web is couched from the cylinder mould in the usual way and is carried by the transfer blanket through the press rolls, which are adjusted as ordinarily, so that a dried felt having the desired compactness will be delivered by the machine. The pressed wet sheet is then dried in the usual way, that is, by passage over steam-heated drier drums, under whose influence the starchy binder in the felt becomes gelatinized and functions to bond the fibers together.

At this point, it might be well to discuss the desirability of maintaining the compactness of the dry felt within a definite range, depending upon whether the felt is to be bituminized for roofing or for flooring purposes. In connection with roofing, where it is desired that the felt absorb the maximum amount of asphalt, the compactness may be comparatively low,so much so that the felt will be able to absorb up to about 250% to 300% or more of its own dry weight of asphalt. In such case, we may prepare felts having a compactness range from about 35 to about 45. When felts for flooring purposes are in view, the compactness should be higher, in order that the bituminized felts may have the desired mechanical properties, especially resistance to indentation or distortion, without being so dense that difficulties will be encountered especially during impregnation. For flooring purposes, therefore, our felts are preferably preparedso as to have a compactness ranging from about 50 to 70.

The felts prepared as hereinbefore described may be put through a bituminizing operation, such as is currently practised in the roofing and flooring industries. The bituminized roofing felt may, as already indicated, contain up to about 250% to 300% or more of its own dry weight of asphalt, whereas the bituminized flooring felt may contain much less asphalt, say only 100% to 175%, more or less, of its own dry weight of asphalt. The bituminized roofing felt may then be finished in the usual manner, depending upon whether roll roofing or roofing shingles are in view. So, too, the bituminized flooring felt may be finished in accordance with the desired practice, for instance, the conventional finishing steps employed in flooring manufacture.

In order to demonstrate the advantages realized through the use of starch or similar binder in the felt, we present hereinafter tables showing the characteristics of various raw felts and bituminized felts prepared from preferred furnishes lacking the binder and preferred furnishes containing the binder.

Raw or unimpregnated felt Com- Ten Basis Ihlck- Tear Manweight ness dry drel 05 7 R.L.T 6 s asqgmg 251 58 43.3 15.0 12{ 7S 62l %R.L.T 33 /%rag 257 00.9 43.8 10.0 .18 0.8:. 4%R.Ps

05%.4 .1 0s. 3mm "J 250 61.0 42.4 12.2 14{ 78 co R.L.I.. 33, %rag 238 54.3 43.8 25.0 24 0.x. 7% R.P.S 601/2%A 33%%rag 250 58.0 43.0 24.8 21 0.x. 7%12.1 .s

Bitumz'nized felt I Ten- Stiif- Elonga- Sat. LT R'T' sile ness tion s5%,R.L.T {w 8.5 29.5 84.2 22.0 04 35%rag a 7.0 48.0 23.0 13.0 108 Q g jE- {w 8.1 37.4 51.0 35.4 10.8 a 8.1 44.5 29.0 22.4 12.5

55%.4 {w 9.2 27.5 42.0 25.0 13.8 35%rag a 7.4 31.8 21.0 10.0 12.5

w 8.6 20.2 45.4 25.0 10.8 if 'gffig {a 7.0 33.3 27.0 10.0 10.8

1 07 gggggg1?: {w 5.7 33.6 48.4 32.0 0.4 a 7.3 35.5 50.0 19.0 12.5

vs I 70A 230 [w 7.0 21.8 53.4 00.0 10.8 [a 8.5 22.2 28.4 17. 12.5

In the foregoing tables, the first column indicates the raw materials which entered into the various felt-making furnishes. The abbreviation R. L. T. signifies a kraft pulp which was refined in comparatively cold, concentrated caustic soda solution and which was used in an unbleached condition in the felt-making furnish. 'I'heabbreviation A signifies a sulphite pulp which was refined in a comparatively hot, dilute, caustic soda solution and which was used in an unbleached condition in the felt-making furnish.

Both these pulps, as hereinbefore indicated, were maintained in substantially unhydrated condition, whereas the rags were, as previously described, beaten or reduced to form pulp or halfstuff. The abbreviation R. P. S. signifies raw potato starch.

We shall now explain the headings of the va rious columns given in the first table. The first heading, Basis weight, represents the weight in pounds of 480 sheets whose dimensions are 24 by 36 inches, this being equivalent to 2889 square feet of sheet material. The second heading, Thickness, represents the thickness of the felt in thousandths of an inch. The third heading, "Compactness," represents-the basis weight of the felt, divided by the thicknessof the felt in hundredths of an inch. The fourth heading, Tensile dry represents the tensile strength of the dry felt in the direction along the papermaking machine. The strength is given in pounds per width of strip. The fifth heading, Tear dry, represents the tear resistance of the dry felt in the direction across the papermaking machine and is given in arbitrary values. This is an important value because, in being led through the machine, the tendencyis to rupture the sheet crosswise, on account of its being pulled in a longitudinal direction. Thus, an uneven longitudinal tension or pull on the'sheet will tend to open up the sheet at one-edge. The sixth heading, Mandrel, is indicative of the flexibility or pliability of the felt. Testing was done by coiling or winding the felt about mandrels of various diameters. Those felts marked 0. K. were of sufficient flexibility to be wound about a mandrel of a diameter as low as 2 inches without cracking, whereas the others showed distinctcracking about a mandrel of the samesmall diameter.

We shall now discuss the headings of the various columns in the secondtable. The first heading, Sat., represents the per cent. saturation which the felt is capable of undergoing without having a superfluity as asphalt. The values given were obtained by noting the per cent. of the usual roofing asphalt impregnant, based on the weight of dry felt, picked up by the felt when immersed for 15 seconds in a bath of such asphalt at 400? F. The second heading, I. T., represents the initial or starting tearresistance of the bituminized felt in arbitrary values. The third heading, R. T.,' is the running tearresistance of the bituminized felt, expressed in arbitrary values. The fourth heading, Tensile, represents the tensile strength of the bituminized sheet in terms of pounds per inch width of such sheet. The fifth heading, Stiffness, represents the stiffness modulus of the bituminized sheet, which was evaluated by noting the load required to elongate a strip of /27 width 2% .of its originallength. The sixth heading, Elongation, represents the elongationin per cent. at the maximum point of loading on the stress-strain curve or diagram. It is to be observed that the values in the second, thir fourth, fifth and sixth columns are given for both direction of the papermaking machine, that is, in the longitudinal direction of hances the tensile strength and tear resistanceof "and in some the raw or unimpregnated felt, but greatly ap -l preciates its ability to withstand fiexure without cracking. It is to be observed that this improvement was realized even over a felt which, although lacking the starchy binder, was prepared from advantageous felt-making furnishes, that is, furnishes containingv rag pulp. It is to be observed, further, that the qualities of the bituminized felt are, on the whole kept unimpaired instances somewhat improved through the inclusion of the starchy binder in the felt-making furnish.

The improvement effected in the raw, unimpregnated felt, especially in its flexibility and tear resistance, is of vital importance, in that during the saturating and finishing operations the felt generally undergoes flexing about a great many rollers of comparatively small diameter. When a felt is made practically wholly from refined but substantially unhydrated wood pulp, the flexing which it undergoes, as hereinbefore described, it apt to cause checking or cracking of the felt, owing to the tendency of the fibers to separate or part from one another under flexing and/or tension. This tendency is partially offset by the inclusion of rag pulp in the feltmaking furnish, but it may, for all practical purposes, be done away with entirely by using starchy or similar binders in the felt-making furnish, particularly a furnish which is made up of a preponderant proportion of refined but substantially unhydrated wood pulp and a subordinate proportion of rag pulp, as hereinbefore described.

The refined cellulose pulps employed in accordance with our invention are produced by taking the ordinary wood pulps of commerce, such as sulphite and kraft, and putting them through the refining action of an alkaline-liquor under suitable conditions of temperature, time, and concentration of alkali in the liquor. Thus, the refined wood pulp may be one which has been prepared by subjecting an unbleached chemical wood pulp, such as sulphite, to the action of hot solutionsof caustic soda or equivalent alkaline refining agents in moderate concentration. Or the refined wood pulp may be one which has been prepared by exposing chemical wood pulp,

such as unbleached sulphite or kraft, to the ac tion of alkaline liquors at about room or even lower temperatures, whose alkalinity is comparatively high and so iscapable of extracting nonalpha celulose components from the fiber under such temperature conditions. In some instances, the refinement of the pulp may take place in alkaline liquors of such high alkalinity and/or atsuch low temperature as to result in an incipient or complete mercerization, as well as refinement of the fiber. This latter effect, that is, mercerization, is had through the use of caustic soda solutions of about 15% or'greater strength, at room temperature, or through the use of solutions' of lower causticity at lower temperatures. A refined pulp whose refinement has been brought about through the use of strong alkaline refining liquors, e. g.. liquorsof sufiicient strength to be mercerizing, is of a puffy and resilient or springy character, and consequently must be handled on the felt-forming machine somewhat differently than other types of refined pulps. The felts formed from such pulps in admixture with ragpulp may require considerable squeezing or compacting while they are in freshly formed condition on the wet end of the feltforming machine, in order to be delivered from the dryend of the machine at a compactness such as is desired in the roofing and/or flooring industries, especially the latter industry. Otherwise, they may be too soft and spongy and, after being bituminized, lack the required firmness and defacement-resisting qualities desired more particularly in a fioor covering material. As hereinbefore noted, however, our felts are in all cases composed largely of the refined but substantially unhydrated wood pulp, irrespective of whether such pulp has become incipiently or completely mercerized during the previous refining operation, or has been preserved in an unmercerized condition.

Inasmuch as refined wood pulp is an essential component in the bituminized sheets of our invention, we wish to define what we mean by the expression refined wood pulp," so that it may be understood in the patented claims and their scope be ascertainable. This expression is meant to exclude the ordinary wood pulps of commerce, such as sulphite, kraft, and soda, whose alpha cellulose content is invariably below 90%. It is designed to include only those preliberated pulps which have undergone refinement or purification in alkaline liquors to an alpha cellulose content upwards of 90% as the lower limit. The refined wood pulp to be used ,in the felt-making furnishes hereinbefore described may be one having an alpha cellulose content of about 94%, as this represents a pulp which can be produced economically and yield excellent results. Refined wood pulps of higher than 94% alpha cellulose content may perhaps be employed to better advantage, but their cost of preparation is higher, and on this account their use ordinarily does not appear to be warranted. It is evidently the removal of that portion of nonalpha cellulose components of preliberated wood pulp, such assulphite and kraft, that conduces to the most marked improvement in the bituminized sheets whose felt base contains the refined wood pulp as a preponderating ingredient. In other words, the overall improvement curve for our bituminized sheets rises sharply asthe preliberated wood pulp component undergoes the initial stages of refinement. In any event, however, it is necessary to stay within the range of wood pulps whose alpha cellulose content is above in order to arrive at bituminized sheets answering the requirements of our invention.

While it may be possible to treat preliberated cellulose pulp from other sources, such as cotton, flax, manila, hemp, ramie, sisal, and the like, as by suitable treatment with alkaline liquors, and to utilize the principles of the present invention in producing the results of the present invention, e. g., utilizing the principle of forming a felt from a refined but substantially unhydrated cellulose pulp containing a pulverulent binder, or from a mixture made up of a preponderant proportion of the refined but substantially-unbeaten or unhydrated cellulose pulp, a subordinate proportion of the unrefined rag pulp or rag halfstufi prepared in the beater engine, and a pulverulent binder, nevertheless refined wood pulps present certain economic and technical advantages, and

hence are to be preferred in the felt-making furnishes of our invention. Oneof the advantages of refined wood pulps, for instance, is their comparatively short fiber length, which permits, with a minimum of effort, equipment, and cost, the production of felts possessed of fine-grained, smooth surface texture. A bituminized sheet prepared from such felt can be directly and economically finished to produce a flooring, for example, having an ornamented face free from imperfections or blemishes.

We claim:

1. A furnish especially adapted for making waterlaid felts, comprising refined but substantially unhydrated cellulose pulp, hydrated cellulose pulp, and a powdered binder.

2. A furnish especially adapted for making waterlaid felts, comprising refined but substantially unhydrated wood pulp, rag pulp, and a powdered binder.

3. A furnish especially adapted for making waterlaid felts, comprising a preponderant proportion of refined but substantially unhydrated cellulose pulp, a subordinate proportion of rag pulp, and a powdered binder in amount not exceeding about 10% of the dry weight of both fibrous components.

4. A furnish especially adapted for making waterlaid felts, comprising a preponderant proportion of refined but substantially unhydrated cellulose pulp, a subordinate proportion of rag pulp, and a starchy binder in amount not exceeding about 10% of the dry weight of both fibrous components.

5'. An absorptive, waterlaidfelt containing as a principal raw material refined but substan-.

tially unhydrated cellulose pulp and a powdered binder.

6. An absorptive, waterlaid felt containing as a principal raw material refined but substantially unhydrated cellulose pulp and a powdered binder in amount not exceeding about 10% by weight of the fiber content of said felt.

'7. An absorptive, waterlaid felt containing as a principal raw material refined but substantially unhydrated cellulose pulp and a starchy binder in amount not exceeding about 10% by weight of v the fiber content of said felt.

8. An absorptive, waterlaid felt, comprising refined but substantially unhydrated cellulose .pulp, hydrated-cellulose pulp, and a powdered binder.

9. An absorptive, waterlaid felt, comprising a preponderant proportion of refined but substantially unhydrated cellulose pulp, a subordinate proportion of rag pulp, and a powdered binder in amount not exceeding about 10% of the dry weight of both fibrous components.

10. Anabsorptive, waterlaid felt, comprising a preponderant proportion of refined but substantially unhydrated cellulose pulp, a subordinate proportion of rag pulp, and a starchy binder in amount not exceeding about 10% of the dry weight of both fibrous components.

11. A process which comprises refining cellulose pulp in an alkaline liquor to higher alpha cellulose content, mixing such refined pulp while preserving it in substantially unhydrated state with a pulverulent binder, and forming a waterlaid felt from the mixture.

12. A process which comprises refining cellulose pulp in an alkaline liquor to higher alpha cellulose content, mixing such refined pulp while maintaining it in substantially unhydrated state with a pulverulent binder in amount 'not exceeding about 10% of the dry weight of the pulp,'and forming a waterlaid felt from the mixture.

13. A process which comprises refining cellu-- lose pulp in an alkaline liquor to higher alpha cellulose content, mixing such refined pulp'while maintaining it in substantially unhydrated state with a starchy binder in amount not exceeding about 10% of the dry weight of the pulp, and forming a waterlaid felt from the mixture.

14. A process which comprises refining cellulose pulp in an alkaline liquor to higher alpha cellulose content, mixing such refined pulp while,

maintaining it in substantially unhydrated state with a subordinate proportion of hydrated pulp and a binder, and forming a waterlaid felt from the mixture.

15. A process which comprises refining cellulose pulp in an alkaline liquor to higher alpha cellulose content, mixingsuch refined pulp while maintaining it in substantially unhydrated state,

with rag pulp and a binder, and forming a waterlaid felt from the mixture.

16. A process which comprises refining prelib-- erated chemical wood pulp in an alkaline liquor to higher alpha cellulose content, mixing such pulp witha subordinate proportion of rag pulp and a pulverulent binder in amountnot exceeding about 10% by weight of the fibrous mixture,'

and forming a waterlaid felt from the mixture.

17. A process which comprises refining preliberated chemical wood pulp in' an alkaline liquor to higher alpha cellulose content, mixing such pulp with a subordinate proportion of rag pulp and a starchy binder in amount not exceeding about 10 by weight of the fibrous mixture, and forming a waterlaid felt from' the mixture;

18. A process whichcomprises refining cellulose pulp in an alkaline liquor toJhigher alpha cellulose content, mixing such refined pulp while preserving it in substantially unhydrated state with a pulverulent binder, forming'a waterlaid felt from the mixture, and impregnating the felt with a secondary binder.

'19. A process which comprises refining cellulose pulp in an alkaline liquor to higher alpha cellulose content, mixing such refined pulp while maintaining it in substantially unhydrated state with a subordinate proportion of hydrated pulp and a binder, forming a waterlaid felt from the mix- 'of an absorptive, waterlaid felt containing refined but substantially unhydrated cellulose pulp, hydrated cellulose pulp, and a powdered binder.

23. A bituminized sheet whose base consists of an absorptive, waterlaid felt comprising a preponderant proportion of refined but substantially unhydrated cellulose pulp, a subordinate proportion of rag pulp, and a powdered binder in amount not exceeding about 10% of the dry weight of both fibrous-components.

Mn'roN o. SCHUR. WALTER L. HEARN. 

